Process for the manufacture of fine particle size titanium dioxide by reacting titanium tetrachloride with oxygen

ABSTRACT

The disclosure is of an improved method for producing a pyrogenic TiO 2 material by the vapor phase reaction of gaseous titanium tetrachloride with oxygen in the presence of hot gases produced by combustion of carbon monoxide and oxygen wherein all the oxygen required for the reaction is introduced in admixture with carbon monoxide, the gaseous TiC14 being introduced into the reaction chamber as one or more rotating jetstreams each surrounded by a mantle of gaseous carbon monoxide which reacts with the surrounding hot combustion gases plus free oxygen to produce a spatially fixed circular flame at a predetermined distance below the point of introduction of each rotating stream of gaseous TiC14 as a consequence of which the reaction of the gaseous TiC14 and free oxygen always takes place at substantially the same location, i.e., reaction zone in the reaction chamber and owing to the rotary movement of each TiC14 jetstream the reaction zone is relatively short as a consequence of which the residence time of the TiO2 particles formed therein is short and of substantially equal duration thereby producing a uniform finegrained product. The disclosure also includes apparatus for reacting the gaseous components in the manner hereinabove described wherein the gaseous TiC14 is introduced into the upper end of a reaction chamber through one or more of concentric tube feedpipes mounted in a gas-permeable plate having a multiplicity of gas passages surrounding the TiC14 feedpipes through which passages mixtures of CO and oxygen at reacting temperature are introduced into the reaction chamber to provide hot combustion gases plus free oxygen for effecting the reaction of the gaseous TiC14 and oxygen. The upper end of the reaction chamber is also provided with inlet pipes for introducing a cold gas tangentially into the chamber for sweeping the walls free of TiO 2 deposits.

United States Patent Hilgers et al.

[ 1 Mar. 7, 1972 I541 PROCESS FOR THE MANUFACTURE OF FINE PARTICLE SIZE TITANIUM DIOXIDE BY REACTING TITANIUM TETRACI-ILORIDE WITH OXYGEN [72] Inventors: Giovanni Hilgers, Post Bechen; Gerard Hitzemann, Post Durdorf; Achim Kulling, Opladen, all of Germany Titangesellschatt mbH, Leverkusen, Germany [22] Filed: May 27, 1970 [21] Appl. No.: 40,920

Related US. Application Data [62] Division of Ser. No. 756,107, Aug. 29, 1968, Pat. No.

[73] Assignee:

Primary ExaminerEdward Stern Att0rneyCharles F. Kaegebehn, Robert L. Lehman and Harold L. Gammons [57] ABSTRACT The disclosure is of an improved method for producing a pyrogenic TlOg material by the vapor phase reaction of gaseous titanium tetrachloride with oxygen in the presence of hot gases produced by combustion of carbon monoxide and oxygen wherein all the oxygen required for the reaction is introduced in admixture with carbon monoxide, the gaseous TiCl, being introduced into the reaction chamber as one or more rotating jetstreams each surrounded by a mantle of gaseous carbon monoxide which reacts with the surrounding hot combustion gases plus free oxygen to produce a spatially fixed circular flame at a predetermined distance below the point of introduction of each rotating stream of gaseous TiCl, as a consequence of which the reaction of the gaseous TiCl, and free oxygen always takes place at substantially the same location, i.e., reaction zone in the reaction chamber and owing to the rotary movement of each TiCl, jetstream the reaction zone is relatively short as a consequence of which the residence time of the TiO particles formed therein is short and of substantially equal duration thereby producing a uniform fine-grained product. The disclosure also includes apparatus for reacting the gaseous components in the manner hereinabove described wherein the gaseous TiCl, is introduced into the upper end of a reaction chamber through one or more of concentric tube feedpipes mounted in a gaspermeable plate having a multiplicity of gas passages surrounding the TiCl, feedpipes through which passages mixtures of CO and oxygen at reacting temperature are introduced into the reaction chamber to provide hot combustion gases plus free oxygen for effecting the reaction of the gaseous TiCl, and oxygen. The upper end of the reaction chamber is also provided with inlet pipes for introducing a cold gas tangentially into the chamber for sweeping the walls free ofTiO depositsv I Q Cold 60:

PATENTEDMAR 7 I972 INVENTORS Dr. Giovanni Hilgers AGENT Dr. Gerhard Hi'zemonn Dr. Achim Kulling ooo ooo PROCESS FOR THE MANUFACTURE OF FINE PARTICLE SIZE TITANIUM DIOXIDE BY REACTING TITANIUM TETRACHLORIDE WITH OXYGEN This application is a division of application Ser. No. 756,107, filed Aug. 29, 1968, now U.S. Pat. No. 3,586,489, issued June 22,1971.

BACKGROUND OF THE INVENTION The invention is concerned in general with a process and device for the manufacture of fine particle size titanium dioxide by reacting titanium tetrachloride with oxygen and more particularly to a process in which auxiliary heat for the reaction is supplied by the combustion of carbon monoxide and oxygen. Heretofore this has been done either by introducing the titanium tetrachloride, oxygen and carbon monoxide into a reaction chamber via concentric tubes, in which reaction chamber the carbon monoxide as well as the titanium tetrachloride are reacted simultaneously with the oxygen; or else, the carbon monoxide is reacted with oxygen in a precombustion chamber where the gas mixture is heated as high as possible and this hot gas mixture is then introduced into a second chamber where it contacts the titanium tetrachloride and, as the case may be, additional oxygen.

Also numerous suggestions have been forthcoming according to which the reacting gases are made to flow from a relatively small burner tube into a wide reaction chamber and the reaction is completed in this wide chamber. However in order to obtain titanium dioxide with uniformly fine grain it is necessary that in this procedure the individual gases be quickly mixed with each other and reacted completely in a small reaction zone without the formation of any large reverse-flow of gas. On the other hand, the reaction must not take place directly at the tube orifices or near the chamber wall since in that case titanium dioxide deposits are formed which modify the gas flow conditions in the reaction zone adversely. For this reason the streams of gas must not be too large in diameter nor of too high velocity. The consequence is that only a relatively little amount of titanium tetrachloride may be put through the burner per unit of time. In addition, disturbance in the flow of the gas streams at the place of transition from the small burner to the wide reaction chamber occur rather easily so that the products formed are of nonuniform quality.

In order to overcome these disadvantages it has been suggested that the titanium tetrachloride, oxygen and carbon monoxide be introduced into the reaction chamber via a fairly large number of tubes which enter the reaction chamber over a large cross-sectional area thereof (German Auglegeschrift, Pat. No. 1,036,221). In this manner the titanium tetrachloride is reacted in the presence of auxiliary flame produced by combustion of the carbon monoxide. Hence high temperatures are developed at the orifices of the tubes and consequently deposits of titanium dioxide start to form in their immediate propinquity and quickly close up the tube orifices. Also the tube orifices are exposed to the hot reaction gases which may result in their rapid destruction.

Efforts have been made to avoid premature reactions of this nature by introducing the titanium tetrachloride and oxygen separately by means of an intermediate layer of carbon monoxide or an inert auxiliary gas. In the one case all gases are introduced in laminar flow into the reaction chamber (Dutch Pat. application No. 6,509,025) but it has been found that the flow rates of the individual gas streams must be adjusted very exactly to each other. Moreover a very long reaction zone is produced as a consequence of which the titanium dioxide particles produced have difi'erent and, in general, too long residence times so that the product becomes nonuniform and too coarse. In another case at least one of the streams of gas is given a rotary movement (Swiss Pat. No. 276,037) whereby the reaction retardation is, indeed, nullified. However owing to the fact that all of the carbon monoxide is reacted simultaneously with the titanium tetrachloride high temperatures develop near the burner mouth so that the protection of the burner orifices intended by the intermediary gas layer is ineffective unless a large amount of inert gas is used. This however has the disadvantage of effecting dilution of the reaction product gases whereby their reuse for production of titanium tetrachloride is rendered difficult. In addition, the ignition of the gases does not always take place at the same place owing to the intermediate gas layer and the relatively low temperature of the oxygen which contribute to the production of titanium dioxide of poor quality.

In still another case all of the carbon monoxide has been reacted with oxygen in a precombustion chamber (British Pat. Nos. 1,010,061 and 1,047,713) as a consequence of which very high temperatures occur in the precombustion chamber, i.e., up to 2,000 C., and hence this must be manufactured of special refractory materials. Moreover the reaction of the gases takes place throughout a long reaction zone with the result that the titanium dioxide is nonuniform.

SUMMARY OF THE INVENTION The present invention relates to improved vapor phase process for producing pyrogenic TiO material by reacting TiCl, with oxygen in the reaction zone of a reaction chamber wherein auxiliary heat for the reaction is supplied by burning CO with oxygen in the presence of an inert gas, as the case may be, the process being characterized in that the carbon monoxide together with all of the oxygen required for the reaction are admixed within a manifold mounted on the upper end of the reaction chamber and pass down through a gaspermeable plate from which the admixed gases plus free ox.- ygen issue into the reaction chamber as a hot mixture of CO and oxygen in substantially laminar flow and at low velocity. The gaseous TiCl, is fed into these hot combustion gases via one or more feedpipes which give a rotary movement to the streams of TiCl each stream of TiCl, gas being surrounded by a concentric mantle of CO, and an inert gas as the case may be, wherein the CO serves to initiate the reaction of the TiCl with the fire oxygen in the hot combustion gases. The incoming streams of gaseous TiCl are thus surrounded by substantially fixed circular flames which are of relatively short length and delineate a relatively short reaction zone in the upper end of the reaction chamber as a consequence of which the residence time of the individual particles of TiO in the reaction zone is short and of equal duration thereby producing a product of uniform grain size.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary elevation in section of the upper end of a reaction chamber showing details of the burner manifold mounted thereon;

FIG. 2 is a plan view of the reaction chamber on line 22 of FIG. I; and

FIG. 3 is an enlarged fragmentary elevation in section of the upper end of the reaction chamber of FIG. 1 showing details of one of the TiCl, feedpipes mounted therein.

DESCRIPTION OF THE PREFERRED EMBODIMENT The preferred embodiment of the invention is illustrated in the drawings wherein the reaction chamber 1 is shown having a top end-closure, hereinafter referred to as a gas-permeable plate 2. The latter is preferably made of a refractory ceramic material and may be a gas-permeable ceramic frit or the plate 2 may be constructed with a plurality of gas passages 10 increasing in diameter uniformly from the top of the plate to the bottom thereof (see especially FIG. 3). A mixture of CO and O is adapted to be fed through the gas-permeable plate 2 from a burner manifold surmounted thereon and to issue from the permeable plate 2 into the reaction chamber 1 in the form of a plurality of individual jets of a hot mixture of CO and oxygen, in laminar flow and at relatively low linear velocity. In fact the linear velocities of the several gas streams are sufficiently low that the individual streams combine almost instantly upon entering the reaction chamber to form a single homogeneous stream of hot combustion gas plus free oxygen having practically no turbulence and filling the entire crosssectional area of the reaction chamber. This same form of homogeneous gas stream will be produced when using a ceramic frit in lieu of a plate having gas passages formed therein. The hot combustion gases will attain a temperature of over about l,0O C.

The gaseous titanium tetrachloride is adapted to be blown into these homogeneous hot combustion gases in the form of one or more TiCL, gas streams having rotary movement. Moreover each titanium tetrachloride jet is adapted to be surrounded, as hereinafter described, by a mantle of CO and an inert gas, as the case may be, which react with the hot combustion gases containing free oxygen to form a spatially fixed circular flame which begins several millimeters below the point of introduction of the titanium tetrachloride jetstreams. By means of these circular flames the reaction of the titanium tetrachloride with free oxygen occurs always at substantially the same location. Owing to this fact and the homogeneous nature of the hot combustion gases, the reaction runs very uniformly and a good product is obtained.

One advantage of the process according to the invention is seen in the possibility of employing burners having any desired large cross section wherein optimal reaction conditions prevail throughout. Moreover, it is possible to process large amounts of titanium tetrachloride per unit of time. Practically no deposits of titanium dioxide are formed either on the gaspenneable plate or at the TiCl, tube mouths. Also owing to'the largely laminator flow conditions prevailing in the propinquity of each titanium tetrachloride jet, no disturbing back currents occur. And further, owing to its rotary movement each titanium tetrachloride jet is mixed rapidly with the hot gases containing free oxygen and reacted therewith within a relatively short distance so that only short and largely equal residence times results for the titanium dioxide particles as a consequence of which the TiO product formed is fine grained and very uniform.

Owing to the fact that only a part of the total carbon monoxide required is burned within the burner manifold located above the gas-permeable plate only moderately high temperatures are reached and hence it is, therefore, possible to employ any type of ceramic material for the gas-permeable plate; in addition to that the danger of backfiring through the inlet ends of the gas passages is out of the question owing to the low carbon monoxide content. It has been found advantageous from a material point of view to introduce only so much carbon monoxide into the burner manifold that by its combustion the temperature of the gas-permeable plate is between 1,000 and l,700 C. The amount of carbon monoxide fraction to be set through the gas-permeable plate 2 for this purpose depends on the size of the burner, on the amount of titanium tetrachloride to be reacted and on the kind and volume of the inert gases sent through additionally, and may be easily determined by experiments. If, for example, a total of 40 parts by volume of carbon monoxide must be reacted with 100 parts by volume of oxygen, then, at normal load in the reaction chamber, 20 parts by volume carbon monoxide may be fed through the gasperrneable plate and 20 parts by volume carbon monoxide via the mantle jets surrounding the TiCl jets. With a'high load in the reaction chamber 30 parts by volume carbon monoxide may be added through the gas-permeable plate and parts by volume via the mantle jets.

Carbon monoxide and oxygen are advantageously mixed with each other prior to being fed through the gas-permeable plate 2, however, it is possible to introduce both gases separately. In the former case, and when using a gas-permeable plate 2 having apertures 10 formed therein (see FIG. 3) it has been found beneficial to gradually enlarge the diameters of these apertures 10 in the manner of a diffuser. An abrupt increase in the diameters of the apertures 10 is not as desirable from the point of flow techniques but is also possible. Owing to the small cross section of the entrance ends 11 of these apertures 10, or by the small cross section of the apertures in a ceramic frit, a backfiring of the flames is avoided. By using diffuser type apertures the velocity of the gases issuing therefrom is reduced (by the continuous increase of the cross section of the apertures) so that the gas flow is largely laminar when emerging from the gas-permeable plate 2. Besides that, no gas is sucked into the exit ends of the apertures by injector effect from the reaction zone.

In addition to carbon monoxide and oxygen, an inert gas may be fed into the gas-permeable plate, for example, nitrogen, chlorine or a reaction product gas freed of titanium dioxide, for additional lowering of the temperature in the plate. In this manner at least a part of the oxygen may be replaced by air.

It has also been found that the characteristics, in particular the particle size of the titanium dioxide formed may be affected by the amount of gas introduced into the reaction zone via the gas mantle surrounding the TiCI jet. It is, therefore, particularly advantageous to mix an inert gas, for example, nitrogen, chlorine or a reaction product gas freed of titanium dioxide and cooled down, with the carbon monoxide forming the gas mantle. The amount of inert gas may be up to about percent by volume of the carbon monoxide which is added in the mantle gas. In this respect it has been found that the particle size of the titanium dioxide decreases with an increase in the amount of inert gas added. The particle size of the TiO may also be modified by the velocity of each mantle jet.

The required rotary movement of the incoming jets of titanium tetrachloride is affected by introducing the titanium tetrachloride tangentially into the upper end of each TiCl, feedpipe.

The wall of the reaction chamber may be rinsed by tangentially introduced cold gas and thereby be kept free of titanium dioxide deposits.

The titanium tetrachloride is introduced in the form of vapor. A certain preheating of the titanium tetrachloride above its boiling point is possible. In order to improve the properties of the titanium dioxide formed, small amounts of additional substances may be added to the titanium tetrachloride in a manner known as such, for example, aluminum chloride, silicon tetrachloride, zirconium tetrachloride or steam. The other gases, i.e., oxygen, CO and inert gases, if used, may also be preheated; it is also specially advantageous under certain circumstances to preheat the oxygen and thereby effect a saving in carbon monoxide.

A preferred device suitable for carrying out the process according to the invention consists of a vertically arranged reaction chamber, a gas-permeable ceramic plate at the upper end of the reaction chamber having one or more axially arranged TiCl, feedpipes which extend through the permeable plate and terminate somewhat below it. In this connection each feedpipe consists of two concentric tubes fitted within each other but spaced apart to form an annular passage for the mantle gases. A caplike housing is provided on the upper end of the inner tube of each TiCl, feedpipe and provided with one or more tangential inlets for effecting rotary movement to the TiCl as it is fed from' the chamber 9 of the burner manifold into the TiCl, feedpipe.

The preferred device for carrying out the invention is shown in the drawings. The device consists of a vertically arranged cylindrical reaction chamber 1 which is closed at its upper end by a ceramic gas-permeable plate 2. Above the gas-permeable plate 2 is a burner manifold consisting of four horizontal plates 3, 4, 5 and 6 supported in vertically spaced parallel relation ship by the cylindrical wall of the manifold wherein the lowest plate 3 seats directly on the gas-permeable plate 2. There are three interspaces or chambers 7, 8, and 9 between the aforesaid four plates. In this embodiment of the invention the gas-permeable plate 2 is provided with numerous apertures 10 (see FIGS. 2 and 3) which are connected with the lowest chamber 7 by small boreholes 11 formed in the plate 3. The several TiCl, feedpipes 12 extend vertically through axially aligned apertures in the gas-permeable plate 2 and the plates 3, 4 and 5. The plurality of apertures and TiCl feedpipes 12 in the gas-permeable plate 2 occupy a large part of the cross section surface of the reaction chamber but leave a narrow annular zone open near the chamber wall.

FIG. 3 is a fragmentary enlargement of FIG. 1 showing a single TiCL, feedpipe 12 and an aperture 10 with its corresponding small borehole 11 in plate 3. While the hole 11 is cylindrical, the aperture 10 is conical. The TiCl feedpipe 12 consists of two tubes 13 and 14 arranged concentrically within each other and connected to each other at their upper ends by a tight fit. Below this tight fit the inner tube 13 is reduced in diameter to provide an annular gas channel 15 between the inner and outer tubes which channel 15 is connected with the chamber 8 of the burner manifold by several radial openings 16. The inner tube 13 extends above the upper end of the outer tube 14 and is enclosed by a caplike housing 17 having one or more tangential passages 18 connecting the housing 17 with the chamber 9 of the burner manifold. Between the upper edge 19 of inner tube 13 and the top plate 20 of the housing 17 an annular space 21 is formed. The bore of the inner tube 13 is constricted adjacent its lower end and below this construction 22 the bore of the inner tube 13 is widened in trumpet shape so as to form, in effect, a venturi in the lower end of the inner tube 13. The bore of the outer tube 14 is also flared outwardly at the exit end thereof. If necessary, spacing rings 23 may be used for maintaining the inner and outer tubes in concentric relationship.

Referring to FIG. 1 a gas mixture comprising carbon monoxide and oxygen is fed by feedpipe 24 into the chamber 7 of the burner manifold from whence it passes through the small boreholes 11 of the plate 3 into the apertures 10 of the gas-permeable plate 2. Here the combustion of the carbon monoxide takes place. The hot combustion gases containing free oxygen then issue from the gas-permeable plate 2 into the reaction chamber 1. Through feedpipe 25 carbon monoxide which may be mixed with an inert gas, as the case may be, is fed into the chamber 8 of the burner manifold from whence the gas passes through the radial openings 16 of the outer tubes 14 of the TiCl feedpipes into the annular gas channels 15 and from thence into the reaction chamber 1. Through the feedpipe 26 gaseous titanium tetrachloride is fed into the chamber 9 of the burner manifold and from thence through the tangential passages 18 of the housings 17 into the inner tube 13 whereby a rotary movement is given to the gaseous TiCl.,. The flow of gaseous titanium tetrachloride will be restricted by the annular space 21 whereby the TiCl, gas stream will be homogenized as it passes into tube 13 and from thence into the reaction chamber 1.

The widening of the bore of the inner tube 13 at its mouth causes a firm adherence of the stream of gaseous titanium tetrachloride to the tube wall so that here titanium dioxide deposits are avoided with certainty. The reaction gases burdened with the titanium dioxide are discharged from the bottom of the reaction chamber. In order to maintain the reaction chamber wall free of TiO; deposits a cold gas is blown in through several tangential inlets 27.

Referring again to FIG. 3 the tapered sides of the apertures 10 should in general not be inclined more than 20 towards the axes of the apertures. It will be understood however that the apertures 10 may be formed also cylindrically in which case their length should be at least three times their diameter, preferably at least five times. As mentioned above the diameters of the apertures 10 must be essentially larger than the diameters of the corresponding small boreholes 11 in the plate 3 while the boreholes 11 must be large enough to insure an adequate distribution of gas to the apertures 10 and yet small enough to preclude backflring. In general, they should not have a diameter larger than 2 mm.

The venturi-type constriction 22 in the inner tube 13 may be omitted but in any event the cross section of the inner tube 13 at its mouth should always be expanded so as to be at least 1.2 times the cross section of the bore at the narrowest part of the inner tube 13.

The TiCl feedpipes 12 should extend into the reaction chamber 1 a maximum distance of half the diameter of the bore of the inner tube 13. Also tube 13 and tube 14 may terminate in the same horizontal plane or one tube may extend slightly beyond the other tube.

EXAMPLE A device similar to that disclosed in the drawing was employed, wherein a burner manifold having chambers 7, 8 and 9 each having an ID. of mm. was mounted on a reaction chamber 1 the inner diameter of which was mm. The gasperrneable plate 2 had a thickness of 50 mm. and consisted of a refractory ceramic material. Above it was an iron plate 3 of 10 mm. thickness. A TiCl, feedpipe 12 was located at the center of the gas-permeable plate 2 and extended therethrough 5 mm. into the reaction chamber 1. That portion of the TiCl, feedpipe 12 supported by the plate 2 and 3 was surrounded by 24 apertures l0, 11 arranged in the form of concentric circles of 12 apertures each with circular diameters of 40 and 80 mm. respectively. The holes 11 had diameters of 1.5 mm., while the apertures 10 were tapered the uppermost diameter being 3 mm. and the lowermost diameter 12 mm.

The inner tube 13 of the TiCl, feedpipe 12 had a length of mm. and a wall thickness in its cylindrical part of 2 mm. its inner diameter being 18 mm. which was narrowed to 10 mm. by the constriction 22, 25 mm. above its mouth. Below the constriction the bore of the inner tube 13 was flared out in such a way that its boundary surface, in longitudinal section, constituted an are having a radius of 20 mm., the diameter of the bore at its mouth being 30 mm. The housing 17 of the feedpipe 12 had an inner diameter of 71 mm. a tangential opening 18 having a cross section of 80 sq. mm. and an annular space 21 of 5 mm. width. The inner tube 13 and outer tube 14 formed an annular channel 15 2 mm. wide which was connected with chamber 8 by 12 radial openings 16 of 5 mm. diameter each.

Through the feedpipe 24 8 standard cu. m./hr. of a gas mixture comprising 3 parts by volume of oxygen at 250 C. and 1 part by volume of carbon monoxide at 50 C. were introduced into the burner manifold and burned in the apertures 10 of plate 2 to produce hot combustion gases plus free oxygen in the reaction chamber. At the same time 2 standard cu. m. per hr. carbon monoxide of 50 C. was fed into the annular channel 15 while a mixture of 25 kg./hr. titanium tetrachloride and 1.15 kg./hr. aluminum chloride (corresponding to 4 percent A1 0 calculated on the basis of pigment) was fed through inner tube 13 at a temperature of 320 C. into the reaction chamber where the rotating stream of gaseous TiCl was surrounded by a mantle or sheath of CO which ignited to form a flame encircling the TiCl, stream at a predetermined distance below the underside of the gas-permeable plate 2. Here the gaseous TiCl reacted with the free oxygen to form pigmentary TiO In order to maintain the chamber wall free of deposits, a total of 20 standard cu. m./hr. air at room temperature was introduced through four tangential tubes 27.

The reaction was carried out without trouble and was completed at 250 mm. distance from the underside of the gaspermeable plate 2. A rutile pigment of good quality that contained no detectable amounts of anatase (limit of detection for X-ray determination: 0.3 percent) was obtained.

The chamber wall and gas-permeable plate 2 were largely free of titanium dioxide deposits.

The annular space 21 could be varied between 5 and 10 mm. for control of the titanium tetrachloride rotary movement and 25 to 50 kg. per hr. titanium tetrachloride could be put through via feedpipe 12. It is possible, without any difficulty, to process larger amounts of titanium tetrachloride in correspondingly larger devices with a correspondingly greater number of apertures l0, 11 using a plurality of inlet tubes 12.

While this invention has been described and illus,rated by the examples shown, it is not intended to be strictly limited thereto, and other variations and modifications may be employed within the scope of the following claims.

We claim:

1. In a process for producing fine particle size titanium dioxide by reacting gaseous titanium tetrachloride with oxygen in the presence of auxiliary heat produced by combustion of carbon monoxide and oxygen, the improvement comprising: effecting the reaction of the gaseous TiCl. and oxygen in a relatively short reaction zone within a reaction chamber by'feeding gases comprising CO and all of the oxygen required both for combustion of the CO and oxidation of the TiCl into said reaction chamber in the direction of the longitudinal axis thereof via a plurality apertured gas-permeable plate, the diameters of the apertures being enlarged at their exit portions, and in which said reaction chamber the gases CO and oxygen react to produce hot and homogeneous combustion gases and free oxygen, which gases pass through sad gaspermeable plate in substantially laminar flow and at a relatively low velocity, tangentially jet feeding a plurality of rotating streams of gaseous TiCl, into said hot combustion gases concurrently therewith and through a plurality of conduits the outlets of which are expanded, and initiating the reaction of the gaseous TiCl with free oxygen in said hot combustion gases by maintaining a concentric mantle of gaseous CO around each of said rotating streams of gaseous TiCl to form a plurality of spatially fixed circular flames, each of which begins several millimeters below the introduction of the TiCl jetstreams, and whereby backfiring of the flames is avoided and essentially no deposits of TiO,, are formed either on the gas-permeable plate or at the mouths of the conduits through which the gaseous TiCl, is passed.

2. in a process for. producing fine particle size titanium dioxide according to the improvement of claim 1 wherein the CO and oxygen are admixed before being fed to said gas-permeable plate.

3. In a process for producing fine particle size titanium dioxide according to the improvement of claim 1 wherein the temperature of the gas-permeable plate due to combustion of the CO and oxygen therein is maintained in the range of from l,000 to 1,700 C.

4. In a process for producing fine particle size titanium dioxide according to the improvement of claim 1 wherein the combustion of the CO and oxygen takes place in the presence of an inert gas.

5. In a process for producing fine particle size titanium dioxide according to the improvement of claim 1 wherein the walls of the reaction chamber are rinsed by introducing tangential streams of cold gas. 

2. In a process for producing fine particle size titanium dioxide according to the improvement of claim 1 wherein the CO and oxygen are admixed before being fed to said gas-permeable plate.
 3. In a process for producing fine particle size titanium dioxide according to the improvement of claim 1 wherein the temperature of the gas-permeable plate due to combustion of the CO and oxygen therein is maintained in the range of from 1,000* to 1,700* C.
 4. In a process for producing fine particle size titanium dioxide according to the improvement of claim 1 wherein the combustion of the CO and oxygen takes place in the presence of an inert gas.
 5. In a process for producing fine particle size titanium dioxide according to the improvement of claim 1 wherein the walls of the reaction chamber are rinsed by introducing tangential streams of cold gas. 